EXHIBIT 8.2

             [FORM OF OPINION TO BE DELIVERED UPON EFFECTIVENESS.]

                                          July   , 2000

AppNet, Inc.
6707 Democracy Boulevard
Suite 1000
Bethesda, Maryland 20817

    RE:  AGREEMENT AND PLAN OF MERGER AND REORGANIZATION, AS AMENDED DATED AS OF
         JUNE 20, 2000, BY AND AMONG COMMERCE ONE, INC., CONSTITUTION
         ACQUISITION CORPORATION, AND APPNET, INC.

Ladies and Gentlemen:

    This opinion is being delivered to you in connection with the filing of a
registration statement (the "Registration Statement") on Form S-4, which
includes the Joint Proxy Statement and Prospectus relating to the Agreement and
Plan of Merger and Reorganization, as amended dated as of June 20, 2000 (the
"Merger Agreement"), by and among Commerce One, Inc., a Delaware corporation
("Parent"), Constitution Acquisition Corporation, a Delaware corporation and
wholly-owned subsidiary of Parent ("Merger Sub"), and AppNet, Inc., a Delaware
corporation ("Company"). Pursuant to the Merger Agreement, Merger Sub will merge
with and into the Company (the "Merger"). Except as otherwise provided,
capitalized terms not defined herein have the meanings set forth in the Merger
Agreement and the exhibits thereto or in the letters delivered to us by Parent,
Merger Sub and Company containing certain representations relevant to this
opinion (the "Representation Letters"). All Section references, unless otherwise
indicated, are to the United States Internal Revenue Code of 1986, as amended
(the "Code").

    In our capacity as counsel to the Company in the Merger, and for purposes of
rendering this opinion, we have examined and relied upon the Registration
Statement, the Merger Agreement and the exhibits thereto, the Representation
Letters, and such other documents as we considered relevant to our analysis. In
our examination of documents, we have assumed the authenticity of original
documents, the accuracy of copies, the genuineness of signatures, and the legal
capacity of signatories.

    We have assumed that all parties to the Merger Agreement and to any other
documents examined by us have acted, and will act, in accordance with the terms
of such Merger Agreement and documents and that the Merger will be consummated
at the Effective Time pursuant to the terms and conditions set forth in the
Merger Agreement without the waiver or modification of any such terms and
conditions. We have assumed that the Merger will qualify as a statutory merger
under the laws of the State of Delaware. Furthermore, we have assumed that all
representations contained in the Merger Agreement, as well as those
representations contained in the Representation Letters, are, and at the
Effective Time will be, true and complete in all material respects, and that any
representation made in any of the documents referred to herein "to the best of
the knowledge and belief" (or similar qualification) of any person or party is
correct without such qualification. We have also assumed that as to all matters
for which a person or entity has represented that such person or entity is not a
party to, does not have, or is not aware of, any plan, intention, understanding,
or agreement, there is no such plan, intention, understanding, or agreement. We
have not attempted to verify independently such representations, but in the
course of our representation, nothing has come to our attention that would cause
us to question the accuracy thereof.

    The conclusions expressed herein represent our judgment as to the proper
treatment of certain aspects of the Merger under the income tax laws of the
United States based upon the Code, Treasury Regulations, case law, and rulings
and other pronouncements of the Internal Revenue Service (the

"IRS") as in effect on the date of this opinion. No assurances can be given that
such laws will not be amended or otherwise changed prior to the Effective Time,
or at any other time, or that such changes will not affect the conclusions
expressed herein. Nevertheless, we undertake no responsibility to advise you or
your shareholders of any developments after the Effective Time in the
application or interpretation of the income tax laws of the United States.

    Our opinion represents our best judgment of how a court would decide if
presented with the issues addressed herein and is not binding upon either the
IRS or any court. Thus, no assurances can be given that a position taken in
reliance on our opinion will not be challenged by the IRS or rejected by a
court.

    This opinion addresses only the specific United States federal income tax
consequence of the Merger set forth below, and does not address any other
federal, state, local, or foreign income, estate, gift, transfer, sales, use, or
other tax consequences that may result from the Merger or any other transaction
(including any transaction undertaken in connection with the Merger).

    On the basis of, and subject to, the foregoing, and in reliance upon the
representations and assumptions described above, we are of the opinion that the
Merger will constitute a reorganization within the meaning of Section 368(a).

    In addition to your request for our opinion on this specific matter of
federal income tax law, you have asked us to review the discussion of federal
income tax matters contained in the Registration Statement. We have reviewed the
discussion entitled "Material U.S. Federal Income Tax Considerations of Merger"
contained in the Registration Statement and believe that, insofar as it relates
to statements of law and legal conclusions, it is correct in all material
respects.

    No opinion is expressed as to any federal income tax consequence of the
Merger except as specifically set forth herein, and this opinion may not be
relied upon except with respect to the consequence specifically discussed
herein. No opinion is expressed as to any transaction other than the Merger as
described in the Merger Agreement or to any transaction whatsoever (including
the Merger) if all the transactions described in the Merger Agreement are not
consummated in accordance with the terms thereof. In the event that any one of
the statements, representations, warranties, or assumptions upon which we have
relied to issue this opinion is incorrect, our opinion might be adversely
affected and may not be relied upon.

    This opinion is intended solely for the purpose of inclusion as an exhibit
to the Registration Statement. It may not be relied upon for any other purpose
or by any other person or entity, other than you and your shareholders, and may
not be made available to any other person or entity without our prior written
consent. We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement. In giving this consent, however, we do not hereby admit
that we are in the category of persons whose consent is required under Section 7
of the Securities Act of 1933, as amended.

                                          Very truly yours,

                                          MAYER, BROWN & PLATT

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